The present invention relates to a throw-away insert for use as a cutting blade of a cutting tool, especially suited for use in finish cutting.
It is desirable that chips produced during cutting be broken into as small of pieces as possible. Long chips not broken are not only dangerous but may hamper the cutting operation because they are likely to get entangled with the tool or the workpiece.
Chips produced during finish cutting tend to be narrow and thin because during finish cutting, both the depth of cut and the feed rate are low, It is rather difficult to break such chips. Such difficult-to-break chips have been a major obstacle in robotizing or automating cutting operations.
Various chip breakers have been proposed to effectively dispose of chips produced during finish cutting, for example, in Japanese Examined Utility Model Publication 51-19271, a small spherical protrusion is formed on an inclined rake face near each cutting edge to curl chips when they collide with the protrusion.
Another arrangement is proposed in Japanese Examined Utility Model Publication 57-50004 in which a narrow ridge extends from the center land to each nose portion to break chips produced during light cutting.
In order to respond to the increasing demand for high efficiency in a cutting operation, there is a growing tendency to shorten the cutting time by increasing the feed rate even during finish cutting in which the depth of cut is small. In other words, cutting inserts are used more frequently than before under low-depth, high-feed cutting conditions.
Chips produced under such conditions tend to be narrow and thick and thus are difficult to curl. If the breaker protrusions are provided near to the cutting edges, such chips will be curled sharply by colliding with the protrusions. Such sharply curled chips are likely to cause seizure and clogging, thus increasing the cutting resistance and hastening the tool wear.
The higher the feed rate, the higher the chip flow speed and the more unstable the chip flow angle tends to be. However, the above-described simple breaker protrusion cannot control the chip flow direction effectively. Thus, the chip flow angle tends to vary widely, so that the curl diameter cannot be kept constant. This makes it difficult to curl and break chips.
Conventional inserts are provided with small spherical protrusions or trapezoidal ridges to dispose of chips by causing them to collide with these protrusions and ridges. However, since there is a big difference between the collision energy produced when the feed rate is high and that when it is low, even if the depth of the cut is low, the position, shape and height of the breaker protrusions have to be adaptable to either a high-feed condition or low-feed condition. There has been no insert which is adaptable to a wide range of feed rates.
Many conventional inserts for finish work have breaker protrusions applicable to a low depth of cut and low feed rate. We will describe one of such conventional inserts and how chips are disposed of with such an insert, with reference to FIGS. 9-13.
FIG. 9 shows an insert having a small spherical protrusion 3 provided on an inclined rake face near each nose. A thin chip A produced while the feed rate is low collides with the small protrusion and is curled and broken as shown in FIG. 10. However, a thicker chip A, produced when the feed rate is higher, is likely to be curled sharply as shown by the solid line in FIG. 11. If this happens, the flow of the chip will stop or, such a thick chip may slide on the small protrusion 3 and protrude in a random direction without being curled as shown by the chain line in FIG. 11. FIG. 12 shows an insert having a ridge 8 which extends from a center land 2 toward each nose. Chips are curled and broken by the ridge. With this insert, too, chips produced when the feed rate is high tend to flow in the manner shown in FIG. 13. Thus, this insert has the above-described problem, too.